An optical laser technology is applied to various fields related to a medical biopsy and detection technology, an optical sensor technology, an optical communication technology, and further to a military weapon technology, a microwave wireless communication technology, an industrial marking and cutting technology, and the like.
In particular, a high output pulsed wave laser is widely used in marking, material processing, remote sensing, Fluorescence Spectroscopy, and the like. A high output continuous wave laser is widely used in communication systems, Fluorescence Spectroscopy, imaging including optical coherence tomography (OCT), and the like.
Generally, a laser system for generating the high output pulsed wave or the continuous wave laser uses semiconductor laser of a single longitudinal mode. In particular, a semiconductor diode laser having an external resonator structure satisfies both of convenient wavelength change and narrow linewidth. However, since output of a laser beam is limited to several to tens of mW, a master oscillator power amplifier (MOPA) laser system may be used to obtain a single longitudinal mode laser beam having an output of about hundreds of mW. Here, the MOPA laser system uses the diode laser of the external resonator structure as a master oscillator (MO) and uses a tapered semiconductor gain medium as a power amplifier (PA).
FIG. 1 illustrates a configuration of a conventional high output pulsed wave laser system, which uses a gain switched distributed feedback (DFB) laser diode as a MO and uses a semiconductor light amplifier including InGaAs/GaAsP with a tapered portion of about 3 mm as a PA, thereby obtaining a high output pulsed wave laser beam. The DFB laser diode 11 generates pulses of picosecond. A laser beam emitted by the MO may be collimated by a lens 12, passed through an optical isolator 13, and focused by the lens 12 to a ridge-waveguide portion 14 of the PA. Also, as the laser beam passes through a tapered wave guide 15 of the PA, the output is increased and collected through the lens 12. Accordingly, output characteristic of the laser beam may be understood.
However, such a conventional high output pulsed wave laser system requires expensive equipment and a complicated process for semiconductor processing. Since the system is a bulk type that combines laser beams using a plurality of lenses, combination efficiency may be unsatisfactory. Furthermore, in a linear laser system, the laser beam passes through a PA part of a MO. Therefore, amplification efficiency of the laser beam may not be high.